Island Climate Update 209 - February 2018

Weak La Niña conditions continued in the tropical Pacific during January 2018. Below average sea surface temperatures (SSTs) remained present in the central and eastern equatorial Pacific Ocean but warmed slightly compared to December 2017.

The NINO1 index (near the coast of Peru), which was the most negative with a value below -1.0°C for December 2017, weakened to -0.52°C during January 2018. The NINO3.4 index is negative at -0.68°C (and therefore in the La Niña category), the NINO3 index is at -

0.91°C and the NINO4 index is only very weakly negative (-0.13°C for the month of January 2018 as a whole).

While the ocean-atmosphere system remained consistent with a weak La Niña state during January 2018, some oceanic indicators, such as the upper ocean heat content and related SST values, weakened. Meanwhile, the Southern Oscillation Index (SOI) increased into the La Niña range once again (+0.9 for January 2018 as a whole) after having subsided to neutral values during December 2017. Similarly, the negative zonal wind anomalies that were present in November in the western Pacific Ocean, signalling

enhanced trade wind circulation associated with La Niña conditions, returned during January.

In summary, weak La Niña conditions remain present in the Pacific Ocean, despite weakened oceanic signals during January 2018. The international consensus is that La Niña conditions are now equally likely to persist (50% chance) or decay to ENSO-neutral (50% chance) over the next 3 month period (February– April 2018). The chance for ENSO neutral conditions to occur then increases to 65% during the May – July 2018 period.

Download the PDF: Island Climate Update 208